(a) Field of the Invention
The present invention relates to a method and system of controlling an engine torque of an automatic transmission. More particularly, the present invention calculates a current oil temperature in a torque converter and restricts an engine torque based on the calculated current oil temperature if the torque converter is in a stall state.
(b) Description of the Related Art
An automatic transmission controls a hydraulic pressure by operating at least one solenoid valve according to factors such as vehicle speed and throttle valve opening in order to shift to a target shift speed.
When shifting occurs, an off-going element of the transmission is released from an engaged state and an on-coming element is engaged from a released state. The releasing and engaging are achieved by controlling hydraulic pressure supplied to each element.
When the brake and accelerator pedals are simultaneously depressed when the shift lever is positioned in the D range, the engine speed increases since the accelerator pedal is depressed, but the vehicle does not move since the brake pedal is depressed. The engine generates torque, but the vehicle speed is 0 km/h. This is referred to as a stalled state of the torque converter. In this state, kinetic energy generated by the engine is entirely converted into heat in the torque converter. As a consequence, an oil temperature in the torque converter abruptly rises.
In a conventional automatic transmission, the stalled state of a torque converter is not detected.
When the oil temperature of the torque converter rises above a normal temperature, foam may be generated in the oil and hydraulic pressure applied to a clutch may be low. Therefore, durability of the clutch may degenerate and the vehicle may shift abnormally.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.